At least 94 Islamic State fighters were killed when the US military dropped America's most powerful non-nuclear bomb on ISIS targets in Afghanistan, Afghan officials said Saturday.

"The number of Daesh fighters killed in the US bomb in Achin district jumped to 94, including four commanders," Nangarhar provincial spokesman Attaullah Khogiani told CNN, using an alternative name for ISIS.

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The initial toll given by Afghan officials for Thursday's strike was 36. A statement released Friday through ISIS' media wing, Amaq News Agency, said none of the terror group's fighters were killed or injured.

The GBU-43/B Massive Ordnance Air Blast Bomb (MOAB), nicknamed the "mother of all bombs" for its extraordinary force, was dropped at 7:32 p.m. local time Thursday, according to four US military officials with direct knowledge of the mission. A MOAB is a 30-foot-long GPS-guided munition.

The strike targeted a network of fortified underground tunnels that ISIS had been using to stage attacks on government forces in Nangarhar province, near the Pakistan border.

The blast destroyed three underground tunnels as well as weapons and ammunition, but no civilians were hurt, Afghan and US officials said.

US military: 'Right weapon, right target'

The US military defended its decision when it was quizzed Friday on whether the 21,600-pound behemoth was necessary for that particular target.

The GPS-guided bomb is capable of destroying an area equivalent to nine city blocks.

"This was the right weapon against the right target," Gen. John Nicholson, commander for US forces in Afghanistan, said at a news conference.

"It was the right time to use it tactically against the right target on the battlefield."

Afghan President Ashraf Ghani said he approved of the strike, and it was designed to support Afghan and US forces conducting clearance operations in the region.

But former President Hamid Karzai accused the United States of using Afghanistan as "a testing ground for new and dangerous weapons."

'Extremely loud boom'

Residents in Afghan villages near the target area felt Thursday's powerful strike.

One resident living around 2 kilometers (1.5 miles) from the blast told CNN he heard an "extremely loud boom that smashed the windows of our house."

"We were all scared, and my children and my wife were crying. We thought it had happened right in front of our house," he said.

"I have witnessed a countless number of explosions and bombings in the last 30 years of war in Afghanistan, but this one was more powerful than any other bomb as far as I remember."

CNN's Ehsan Popalzai reported from Kabul and Laura Smith-Spark wrote from London.